Colonoscopy with whole-colon water exchange method has been shown to be useful for reducing medication used, pain experienced during colonoscopy, increasing the success rate of cecum intubation and adenoma detection rate in sedated and unsedated patients undergoing screening colonoscopy. Exchange of water during scope insertion minimizes loop formation and prevents lengthening and distension of the colon during colonoscopy. This will facilitate the colonoscopy in average or difficult colonoscopy. However, it is not known whether the benefits of water exchange method of colonoscopy was mainly due to its effect on the left colon.